Cable plows of the type disclosed herein have been utilized for many years to lay many types of cables, flexible pipes, conduits, etc. The cable or pipe has been passed into a trench, dug by a plow-blade, through a chute, or some other mechanism for guiding the cable or pipe, which trails the leading edge of the plow-blade. In either case, the cable generally passes into an opening in the ground created by the blade from a spool mounted on the vehicle which pulls the plow apparatus. Because the plow must be pulled through very rough and, at times, heavily packed terrain, the ground-engaging vehicle which pulls the plow apparatus has had to be a very large and powerful tractor.
Vehicles pulling cable plows have generally been required to travel at relatively slow speeds, laying cable at a rate in a range of inches per minute. In this regard, it has been found that vibration, or reciprocating movement of the plow-blade, is effective to work the soil and reduce the tractive pulling force required to pull the blade through the ground. Where such vibration or reciprocating movement of the blade was employed, it was found that smaller tractors possessing less tractive pulling power could be used to lay cable. This ability to use smaller tractors offered several advantages including less ground disturbance, more maneuverability, faster cable laying, greater mobility, etc.
Following the development of vibratory cabling laying plows, however, it became apparent that the vibrations from the plow had a negative effect on the operators of such machinery, and upon the working parts of the vehicle pulling the plow. It proved to be very stressful for operators to be subjected to constant vibrations for long periods of time each day. In addition, the parts of the vehicle tended to come apart and need repeated tightening. The vehicles also seem to wear faster.
Therefore, efforts were made to dampen the vibrations emanating from the plow apparatus. For example, U.S. Pat. No. 3,618,237 discloses a frame support for a cable laying plow apparatus having torque cushioning elements which absorb some of the reciprocable motion of the support in an attempt to isolate the frame from the supporting structure. A four-point support apparatus is also provided to cooperate to define a parallelogram-type linkage apparatus.
U.S. Pat. No. 3,561,539 discloses a vibratory cable plow having a sharpened plow point at an unspecified angle and a plurality of resilient pads designed to enhance vibratory movement and dampen the transfer of vibratory movement from the enlongated plowblade to the mounting frame. Unfortunately, none of these dampening means adequately dampens vibrations from the vibration or reciprocating device.
The vibratory plow apparatus of U.S. Pat. No. 3,561,539 also discloses a parallelogram-type apparatus for raising and lowering the plow while maintaining the plow-blade in a substantially vertical orientation. U.S. Pat. No. 3,684,030 also discloses a parallelogram-type support structure for a plow-blade including a number of digger teeth which project forwardly and downwardly from the plow-blade. Motive mechanisms are also disclosed for swinging the linkage mechanism on a vertical axis with respect to the vehicle, and for lifting the lower arm of the linkage mechanism and hence the plow-blade.
One of the advantages of the parallelogram-type linkage mechanism is that the plow may be raised without changing the vertical orientation of the plow to the soil. As compared to three point linkage mechanisms, this enables the cable plow to continue laying cable at the lowest possible depth when the plow must be raised to traverse over immovable objects such as pipes or large rocks which may be buried in the soil. When a three point lift mechanism is employed, the plow is generally raised such that the plow is angled backwards and away from the vehicle. The backside of the plow-blade where the cable guide outlet mechanism is generally located, is thereby raised to a greater degree than the leading edge of the plow-blade which must traverse across the buried object. Since the backside of the plow-blade angles upward from the leading edge of the plow-blade, the cable can come out of the guide mechanism as much as a foot higher than the leading edge of the plow-blade. The parallelogram-type linkage mechanism allows the plow to be raised vertically without creating this angle, thereby allowing the cable to be laid at the greatest depth possible when traversing over immovable buried objects.
One disadvantage of the parallelogram-type linkage mechanism is that although it enables one to lay cable at the lowest depth possible when traversing over immovable buried objects, it is not possible to maintain the blade at a desired orientation to the ground when traveling through irregular terrain. In irregular terrain, when the vehicle and the plow-blade may simultaneously engage ground at different pitches or slopes, the angle of the plow-blade will depend on the slope of the ground to which the vehicle is engaged. This slope may be entirely different from the slope of the ground in which the plow-blade is engaged. In such a situation, the plow-blade will not be perpendicular to the ground. This can result in the backside of the plow-blade being at a different depth than the leading edge of the plow-blade. If the backside is higher than the leading edge, the cable emerging from the backside can be laid at inconsistent depths in irregular terrain.
It will be appreciated from the foregoing that prior art devices present problems which are in need of solutions. The present invention provides solutions for these and other problems.